Water conservation is a major issue in many parts of the world. In particular, population growth is putting fresh water supplies under tremendous strain. Notably, landscape water usage consumes more than half of the potable water supplies in some areas. Landscape water usage refers to the artificial application of water to promote the growth of desired plants. This is especially true in agricultural areas where crops require frequent watering in order to achieve maximum yield. However, residential, governmental and commercial water usage also significantly taps the available water supply, i.e., yards, golf courses, and parks also demand significant amounts of water to maintain healthy foliage.
In recent years, using in-depth study of soil moisture characteristic of arid and semi-arid areas, meteorological data, evapotranspiration data, optimization theory and fuzzy theory, have proven deficit irrigation as a new promising irrigation method that allows certain cuts in water consumption, especially under the condition of limited water resources.
Because of water-stressed regions, water geographical imbalance and other factors, agricultural water-saving irrigation has become an important breakthrough in agricultural production and the entire international economy. Deficit irrigation is that when water resources are insufficient to meet the full cultivation, the existing water resources are configured optimally for an irrigation system. Deficit irrigation systems involve a lot of mathematical calculations, require large number of input parameters, many of which are difficult to measure. However, this watering technique is becoming increasingly popular among researchers, farmers and authorities.
Currently, irrigation systems are using weather forecast and soil moisture as their main parameters. The most used methods for soil moisture measurement are drying method, TDR method and the neutron method. However, irrigation methods which use weather forecast and soil moisture have major shortcomings: they only measure soil moisture content at individual points which do not accurately reflect the status of soil moisture on a large area as a whole.
The term evapotranspiration (ET) is used in the irrigation field to quantify how much water has been lost from soil through transpiration by plants. An ET value is calculated using actual meteorological data obtained from meteorology stations. The factors typically used to calculate an ET value are temperature, solar radiation, wind speed, vapor pressure or humidity, and barometric pressure. A change in one or more of these parameters can have a direct effect on the ET value used to determine when and how much to water. ET values are usually normalized to a specific type of vegetation. One of these ET values is ETo which is for 4″-6″ tall cool-season grass. ET values are then used in conjunction with other coefficients to determine how much water to apply to replenish the water lost from the soil. Factors that affect determination of the amount of water include the following: (1) type of vegetation; (2) soil type; (3) root depth; (4) topography; (5) micro-climate; and (6) density of vegetation.